


The Butterfly Effect

by MyntheLapine



Category: Eyeshield 21
Genre: Comedy, F/M, Post-Canon, Slice of Life, rated t for Hiruma's mouth mostly, romance here and there if you squint, the f word reigns supreme in this story
Language: English
Status: Completed
Published: 2021-03-06
Updated: 2021-03-06
Packaged: 2021-03-12 02:13:26
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,879
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29877531
Author URL: https://archiveofourown.org/users/MyntheLapine/pseuds/MyntheLapine
Summary: If the flap of tiny wings is supposedly capable of causing a typhoon, one could wonder at the potential for unbridled chaos Hiruma has in mind dragging his little sister to Saikyoudai University and help out as the team mascot, Zappy the Wizard. A timid and introverted creature, we only can question just how much she has in common with the devil himself.
Relationships: Akaba Hayato/Original Female Character(s), Anezaki Mamori/Hiruma Youichi
Comments: 2





	The Butterfly Effect

**Author's Note:**

> I am... admittedly new to the greatness of Eyeshield 21. I always wanted to get into reading it, but it is only in 2021 I found the time and was able to kick my ass into gear. I love it so much and I only wish I knew about it sooner...
> 
> All the same, this is my first fic for the fandom, and even if I read the full manga and have gone back to do further research a bunch, I am not going to say this will be as good as it could be if I were a fan for longer than a mere month or so. I can only hope Mayu-chan is doing an okay job getting tossed in with the insanity and hijinks that Amefuto can offer lol.

There was nothing quite like witnessing firsthand how the utter of a single word was enough to hush a chaotic classroom. Frequent chatter, complaints, and even arguments were all forgotten once it was spoken into existence.

Perhaps not so much a word, but more a name to be precise. One that was attached to the captain and quarterback of Saikyoudai University’s American Football team. A man who, by vague methods, was granted permission to carry firearms on his person like they were no more illegal or out of place than a textbook. Someone who had the headmaster and full staff under his thumb, just putting into perspective a smaller fraction of the higher-ups he had dirt on. Of which included the police, government officials, and perhaps a few world leaders with how much influence and power he had thanks to the little black book of threats and his army of slaves in his arsenal. A kind of guy who was the very last person whose path you wanted to cross.

The devil himself, Hiruma Youichi. And with those sharp teeth almost always in some twisted grin, and the aura that gave you nightmares when you locked eyes with him, he sure looked the part too. There was even a feral canine so ferocious many genuinely believed it could be some kind of hell hound that he kept fed as a sort of deal for it to do his bidding.

The creature that lurked in the doorway after the teacher stepped out for a moment, however, had none of that... 

A young woman stood there instead, twisting her hands anxiously as the many eyes observing her slowly lost their panicked delirium. This ‘Hiruma’ was much smaller, long white bangs hiding all but her mouth that was pressed into a firm line. Even with her eyes hidden behind a curtain of hair and a hood, it was still noticeable her attention was on the ground more than anything. The hoodie she wore was light green with little teeth made of scraps of fabric lining the inside, reminiscent of some kind of crocodile design, being far too cute to be taken seriously.

“What is this, a joke?” someone scoffed.

“False alarm… Almost jumped right out of my skin,” another joked, trying to lighten the mood.

“Are you serious?” still questioned one directly, peeved at the misunderstanding regardless.

The girl said nothing, just clutched the strap of her bag nervously. Not much of a talker it seemed, making more sense now with how it had been someone else introducing her. Not that there was anything she could say in this situation. She didn’t owe them a reason why her name was what it was.

Thankfully they let it go, now ignoring the newcomer just as soon as they saw her. Nothing much besides some poor soul having the same last name as the very embodiment of hell on earth they heard about. And seeing how she wasn’t the one they feared, it was safe to mindlessly chatter again in their eyes. As naïve as first-year college students could be, now they believed the coast to be clear.

Inwardly snorting at their carelessness, Hiruma Mayu settled into a desk a bit further away from the larger group, loud and obnoxious now that their shock was gone. It wasn’t a surprise that person had managed to dupe them so easily into spilling personal secrets about one another, given how they blabbed so much in the open. All it would take is one of them that was observant and petty enough on his list, and soon the whole room would easily crumble into more fodder for the never-ending rumor mill that fueled his book from the start. They probably would be singing a different tune altogether if they knew there was a deeper connection between her and the one they feared so much. However, the longer they stayed in the dark the better. 

Mayu wasn’t interested in having a reputation as Youichi Hiruma’s younger sister being the first thing others knew about her. She was still her own person at the end of the day, and being feared by association did not sit well with her. That, and she would be the first to say that there was little if anything they had in common.

It was already hard enough to connect to others on her own terms. But the less people who knew, the better her chances could be that just maybe by the end of the year, she might make a few friends.

The professor finally returned, spreading a hush across the room as the lecture started not soon after. And as Mayu scribbled notes down, she couldn’t help but be annoyed at whoever it was behind her that quickly tossed an eraser at her head when no one was looking. Someone probably annoyed about the disturbance her introduction caused or some other equally stupid reason.

Still writing, she ignored them. Anyone who had time to annoy others instead of taking the class seriously wasn’t going to last at a high-end level college long. No point in wasting time with that kind of childishness. After all, she had to work hard to earn her keep here. It was already a miracle she managed to get in, even if she felt she didn’t deserve the opportunity.

Mayu was by no means lacking in intelligence. Saikyoudai was just a school at a level where you needed the very finest of records, grades, or connections to attend. And with thanks to a very serious blunder on her end during her first year in high school, she feared it would have been impossible to get her application accepted.

The fact she even had applied had been wishful thinking. Not at all something she had held her breath over. An idea by her father actually, knowing how conflicted she had been on choosing a college to try out for. Showing up to take the entrance exams, there had been so much doubt even as she breezed through the questions. 

It wasn’t just about being smart enough, not for her.

After all, it was no coincidence there had been a strange letter for her alongside her results from the exams. She passed, but her excitement was short-lived seeing as the message from Youichi, who had not bothered to contact her in over a decade, made it clear he had a hand in it.

_**‘Had some shit stains cleared up for you. You can thank me when stopping by the Wizard’s clubhouse on your first day at Saikyoudai.** _

_**P.S. Don’t even THINK about fucking changing your mind, brat!** _   
_**Y.H.’** _

Seeing how there was only one person who could even possibly know her on campus, and his initials matched perfectly, Mayu was one-hundred-and-fifty percent certain it was Youichi. As to why was up in the air, but seeing as this class was the last of the three she was attending for the day, and only to write down basic materials and the schedule, she would be free to find out rather soon.

Another item was tossed at her, and her temper was already building. Snapping her head back, she knew well her glare wouldn’t be seen at all under her long bangs, but she hoped the rather displeased scowl on her lips was enough to get the hint out. The person was some kind of idiot, already feigning innocence like his posture and the cut-up eraser bits in front of him wasn’t enough proof.

“Hmph…” was all she could muster before standing when the bell chimed. The professor didn’t bother stopping her oddly, even as she walked out the door before being fully dismissed. Whether he just didn’t care, was rather lax about students leaving early in general, or some other reason, it didn’t matter. She would apologize later if needed.

All she could feel was glad to take a deep breath and try to find someplace a bit more secluded to relax. At least long enough to not be in a foul mood before seeing what schemes her elder brother had in store.

It had been a long time since she last saw him. When she was still in pre-school at that. And while he used to write once in a blue moon, the last one had been five years ago saying he was never going to come home again.  
But Mayu was at least aware of what kind of person Youichi was, all the same. If rumors were even slightly true, he was just as violent as ever, if not more so. Being on a team for some kind of weird American ball game she didn’t exactly get, but had seen his matches, and knew what people said about him. The guns and him getting a pet were new, but even through a television screen she recognized that wicked grin similar to the one he wore after hitting her on the head for being too loud. Even if his hair was blonde now, it would be hard to mistake him for anyone else.

He had always been insanely clever, even when he was just five. A constant thorn in her mother’s side and someone she was not allowed to play with. Perhaps a good thing, seeing how disinterested he was in everything around him, especially a younger half-sister.

Why now then, was he suddenly so adamant about seeing her?

Having settled onto a wooden bench while still in the same building, there was a sound of music that caught her ears. It was loud, but not something she disliked. Gazing at a pinboard across the hallway from where she sat, Mayu’s mind wandered off as her foot tapped along to the beat.

It did occur to her now that she wasn’t even sure where the sports club she was supposed to go was. Obviously, it had to be the same sport as he played. That… Amefuto?

The best way to find out would be to ask someone else she supposed. And seeing as it would save time, given her lack of confidence in verbal communication, she pulled out her notebook, tore out a piece from the back of it, and wrote down a message beforehand.

_**‘Looking for Amefuto Club. Directions please.’** _

Short, simple, and to the point. The please was a habit of manners, but it didn’t hurt to have it.

It came to her attention the music had stopped at some point, and now that it did she heard the shuffling of feet leaving the room beside the bench she sat on. Hopping up, she took a deep breath before following after the small group of musicians. They might at least have a lead as to where she could start looking.

One of them saw her trailing behind, making the need to call out avoidable as she waved a hand out to get their attention. As he slowed down and turned to look at her, the rest followed his example in noticing the small girl in the crocodile hoodie.

“Oi… what’s up kid?” he asked. His hair was dark and pulled into a low ponytail, facial hair giving him a rugged look. But not unkind, as he gave her a soft grin.

Handing over the slip of paper, she gave him a moment as he read it, watching as he shot a look back at his companions. It appeared as if he was weighing over something heavily in his mind, before sighing in defeat.

“Hey, Hayato-kun… you’re in that American Football club, right? The little lady here needs some help getting there…” he shot at one part of the group.

Reddish-pink hair stood out quite a bit, and as this ‘Hayato-kun’ looked over at Mayu, she froze.

His eyes were an intense shade of red, something she had never seen before on a person. Enough to give her goosebumps as he studied the one his associate was speaking of.

“Fuu… Not a fangirl I presume?” he asked.

Mayu snorted before shaking her head. Taking a deep breath, she forced out “B-bu… Business…” in a gentle, if deep voice. Something she’d once been told made her sound more like a pre-teen boy instead of a girl.

The first guy chuckled. “You always get the quiet ones… Catch ya later man…” he said, leaving the two alone in the hallway to catch up to the rest of his friends.

Great, now she was alone with a stranger whose stare seemed to pierce through her very soul. Thankfully however, he pulled out a pair of blue sunglasses while sighing and the effect of his gaze became significantly less jarring.

“Don’t mind Jiro… His tempo always gets thrown off when around girls,” he explained. “Ah, my manners… I am Akaba Hayato. As you heard, I’m part of the Saikyoudai Wizards.”

Softly nodding, she pointed to herself, muttering “M-Mayu…” as her introduction. It was only fair since he did first.

“Mayu-san… I see. I was just on my way to practice.” Shifting a bit to readjust the strap on his bag holding what may have been a bass or guitar, he pointed down the hallway with his thumb. “If it’s for business only, it shouldn’t be of any harm to take you there.”

Grinning, she couldn’t help but be pleased with her success. Falling into step beside him, Mayu felt even happier at accomplishing basic interaction so well for once. 

This guy was rather nice to talk to, which helped. He wasn’t loud or impatient at least, and so far he was rather alright. If still a bit intimidating.

Walking, she realized pretty soon that the club must be a bit far since the open areas away from the school were still out of sight. Given how sports needed plenty of room to be played, the cluster of buildings was naturally kept at a safe distance. Akaba was keeping a steady pace, but one that wasn’t hard for her much shorter legs to keep up with.

He didn’t say anything, but Mayu didn’t mind it. The less she had to try and force herself to chat was perhaps for the better. To fill the silence she merely studied the scenery and made mental checkpoints for locating things on her own next time, softly humming to herself.

It stopped the second the field was suddenly in front of her, making her steps falter. Very open, and what had to be the clubhouse on the opposite end. 

Her escort noticed she was no longer following, turning back to look at her with a lifted brow. Akaba looked as if he wanted to ask her if she was alright, seeing her right foot still lifted before stepping off of the pavement and onto the grass. He didn’t get the chance however, as Mayu already began moving forward.

She was being silly. She had no reason to be nervous just for walking onto the field here.

And now that she was ahead of him, the red-haired musician let it go as he easily caught up. Still, he couldn’t help but ask “This business you have… what is it exactly?”

Fidgeting with the sleeves of her hoodie, Mayu’s mind raced for some kind of an answer.

This guy was still a stranger even if she knew his name now. It was the worst idea to say she was meeting family, as he may want to pry about who her family was. And despite how silent he was, Akaba could be the type to run his mouth later for all she knew.

In hindsight, she didn’t even know if it was okay to trust him to walk out here in the first place. He may not even be a part of the team and was playing a joke on some naïve freshman.

Mentally smacking her forehead, she told herself it was cruel to suddenly think that way without proof. His behavior so far had been rather polite. He didn’t act like… other people who she knew firsthand did those things. If he were that kind of person, Akaba likely wouldn’t be keeping a respectful distance where she could turn and flee so easily. He wasn’t making small talk to try and ease her into some false sense of security.

All he was doing was letting her follow him, and her anxieties were making things out as something they weren’t. Mayu had promised herself to stop being so paranoid even before deciding to attend this specific school. This was just waylaying that desire due to unfounded suspicions.

“A debt?” she finally said. It was a late reply, but it was technically true. Youichi did say she should thank him for whatever thing he did in that cryptic letter of his. And not unlike how one could receive a ‘gift’ from a person belonging in a criminal group that would demand repayment down the line, it was better now that she had accepted it to nip this favor in the bud.

Even if he had not given her much of a choice in the matter.

Akaba let out a deep, tired sigh. As if this wasn’t anything new, or perhaps some deep disappointment. “Fuu… Even a melody can get lost in the cacophony it seems.”

Mayu wasn’t quite sure what that was supposed to mean, but before she could think longer on it she heard her name being called out.

“Mayu-chan! There you are!” Turning about, a familiar face was running up from behind in the form of her roommate, Mamori Anezaki.

Beneath the white bangs, Mayu’s eyes blinked slowly in confusion. Why was she here? 

They had only met the night before, and even then there hadn’t been much said between them. Not for her senior’s lack of trying, but it was a strange and new environment. Even if the brunette had been welcoming, it had still been a race for Mayu to get the introductions out the way where she could hide in her room to recover and adjust.

It had been too much all at once, hiding being her best defense to overwhelming feelings and situations. A fact she hated, with the consequences such a drastic action left. The world still kept moving even when she withdrew into her shell, and as such, she missed out on many important things.

Exactly why Akaba’s question, even if it clarified the situation, left her with even more of her own. “Are you familiar with her, Mamori-san? Even for the manager, it seems a bit much that you are hunting down one of Hiruma’s clients.”

Mamori too now sighed. “It’s nothing like that, I assure you. I’m glad it was you who helped her find her way, however.”

Akaba smiled, even as he said “It wasn’t anything difficult. Honestly, she found me first.”

Mayu, seeing this was where they would part ways, still mumbled a “Th-thank you…” towards the odd red-head.

“Best of luck,” he shot back before walking towards the large clubhouse.

Mamori then cleared her throat a tad, looking sheepish. “So… I realize I didn’t get a chance to tell you last night about me being the team manager.” Placing her hands together, her blue eyes tried to look back into Mayu’s as best she could. “This morning I was going to mention how I wanted to meet up with you after your classes and take you here myself but… you were already gone.”

Swallowing a lump forming in her throat, she was hit by the feeling that, maybe she missed more than just important information.

Mamori then tried to brush it aside, gesturing to the clubhouse. “It’s no big deal. You are safe and sound, and we should get going so you can rest before you speak with Hiruma-kun.”

Slowly nodding, Mayu went the rest of the way behind her senior, thinking over the night before.

She knew that this girl had not offered a living space to her so easily of her own accord. What sane person would allow a total stranger to share their living space without a good reason? A certain someone had his hand in it, that much Mayu had been certain of.

Something that made her hesitate to accept any of the kindness that had been offered. Such as helping her unpack the pre-delivered boxes or to eat dinner together. Mayu wasn’t exactly a subtle person, blunt even if it came to it. It would be obvious she had been trying to avoid Mamori even if she put major effort into covering it up.

To her, it was suspicious someone was being so friendly to a stranger, and one who came off as so standoffish. Mamori got the hint and let her be the whole time she hid in her room, letting her adjust while taking care of her belongings.

Mayu knew very well she had a way of speaking and reacting that was generally off-putting and had gotten her into trouble before. It was one of her many flaws, and she knew them well. But the more she had been pushed about it, the more she withdrew in the past. 

How anyone who just met her was able to give her so much breathing space and not react negatively to her distancing herself would have to know about her. Maybe even was being blackmailed to put up with her. That, or they had to be some kind of an angel or saint.

She turned down the offers, barely spoke, and looking back on it, she realized she had been overboard in her behavior. Even if it was a new place and person, and her anxiety had been high, it was not fair of her to act so cold. Especially disappearing so early without a word.

Wandering off early in the mornings was something she always did, but she should have been more considerate of the person she would be living with for a while. Mamori seemed to be extremely relieved now that she knew where she was.

As they stepped inside, no one else was there it seemed. Or just not in the same room. Maybe changing for practice.

Flitting her gaze about and absorbing the interior of the room, she almost missed it when Mamori gestured to a table. Or what should have been a table, seeing how littered it was with small figures and other miscellaneous items.

“You can sit here for now. Would you... like some tea while you wait?” the brunette offered.

There was no anger or annoyance. But the fact was, there was some form of hurt in her eyes. It was almost as if she was the one who felt bad for only speaking to her. And she still stood there, patiently waiting for an answer. She was trying to be kind even now, and it made Mayu’s gut twist inside seeing how hard the woman was trying.

“I’m… sorry….” Mayu whispered, feeling genuinely awful despite whatever relationship this woman had with her older brother. “If I… made you worry. And… b-being harsh…”

Taken aback slightly, Mamori looked at her now, a bit stunned. 

Twisting her hands even between the green fabric of her sleeves, it felt very awkward to have someone watch you for so long over an apology. She stared at the tiles under her feet, wishing it was physically possible to vanish into the floor.

It broke once she heard Mamori speak with warmth back in her voice. “I forgive you. We both are still getting to know one another, right Mayu-chan?” 

“Y-yes, Anezaki-senpai…” She was unable to look her roommate in the eyes, even if she felt better admitting to her mistake. She would need to be more thoughtful in her actions from now on if she wanted to put an effort into making friends.

A hand grabbed the top of her head, and at first she thought Mamori was the one doing it. Until Mayu registered the hand grabbing the top of her hood was from behind her, and increasing in pressure slowly but painfully.

“Ow!” she fussed, trying to reach up and grab the hand even as it already vanished. Turning around to glare at the person who did that, she saw a sharp-toothed grin and heard a high-pitched cackle.

“Kekekeke~ You’re in the way, fucking brat!” Hiruma said, shoving Mayu over.

Mamori instantly spoke up, hands on her hips. “It doesn’t help that you didn’t say anything about being behind her Hiruma-kun. At least tell her you are there instead of pushing someone out of the way like that!”

The now-blonde and much taller version of the boy she remembered shrugged without a care. “Not like she’s going to fucking break?”

The brunette seemed to take exception to that, and now Mayu was glad she was out of the way as the two started to argue loudly, with a gun and broom respectively in their hands.

There was a tug on the corner of her jacket, and the table was now occupied by several people. Including Akaba, who was the one who tried to get her attention. “You might as well sit for the interlude. They may take a while…”

Nodding, she took his advice and sat in the empty chair beside him. The rest of those currently seated was a boy probably not much bigger than she was with spiked black hair and a red mark on his forehead. Or was that a mole?

Next to him was another blonde bearing a cross-shaped scar on his cheek, fiddling with a soda can while glancing at the ceiling and ignoring the spat. It appeared he had gotten long used to this. And did he seem a bit… familiar?

Shrugging mentally, she looked at the last two. A man with long white hair and a book in hand who was still reading despite the commotion, and another with shorter dark brown hair watching the two combatants closely. As if waiting to see if he needed to step in.

Mamori seemed to be doing just fine however, sternly lecturing Hiruma without a hint of fear. “You don’t just grab a person by their head and then shove them aside!” she firmly stated, the broom resting at her side, like a war pike ready to deflect and swat at any form of assault. “And furthermore! How is that any way to greet her after making her c-”

A shot fired into the ceiling before he retorted with “She’s my fucking sister! She’s used to this shit.” There was a pause after, as what he just said sank into the atmosphere of the room.

Pulling her hood down, Mayu tried to hide her face. And just like that, her cover was blown.

“Sister?” asked the dark brunette. “Hiruma, you were being honest back during the Christmas Bowl after all? Should I text Achilles so he doesn’t feel like such an idiot after believing you?”

The person with the book chipped in with “It’s probably for the better you don’t…”

Stiffening, Mayu resisted the urge to groan by biting her lip. What the hell did he do? Why was she brought up at a Christmas party? 

Oh, wait… He said ‘bowl’, not ball. That was the name of that really big game back during December a few years ago. Dad had been super excited about it…

But that still was not reassuring in the slightest when he could have said anything! And now there were eyes directed her way and the feeling of her skin crawling was almost bad enough that she wanted to hide under the table and wish this was all just a weird dream.

Not happening as Youichi yanked back her hood, revealing her smaller pointed ears. While she squeaked in protest, he took the opportunity to push the silvery-white bangs out of her face. Her narrowed green eyes glared at him, and as her mouth twisted into a scowl, her small, pointed canines now too were on full display.

Holding her face still, Hiruma turned her exposed features to the group. “See for yourself Fucking Wild Hair. The Fucking Brat gets it honest.” He then cackled as Mayu swatted his hands away once more, taking full delight in her furious pout. “Kekekeke~ Such a devilish temper dear sister!”

“D-dear my foot!” she snapped. Hiding her face in her hands, Mayu resisted the urge to scream. 

He was even more annoying than she remembered. At what point had he matured between the ages of five and twenty? She sure wasn’t seeing it!

His hand grabbing her head again, Hiruma now spoke to the rest of the room. “Seeing as the rest of the dumbasses are late, they can figure it out on their own. This one here,” he emphasized with another squeeze, “is going to be one of our new members.”

Giving up with a sigh, she knew damn well this was the favor he meant. Her head was pounding, be it from the pressure of his grip or a forming headache she wasn’t sure, but two things were clear…

One, her brother was an even bigger jerk-ass than she realized. And two, Mayu was going to be lucky to not flip her shit before the end of her first year.

Was he seriously expecting her to play American Football?!

**Author's Note:**

> Welcome Mayu, to hell! :D
> 
> Jk jk... Stay tuned for chapter two at some point lol.


End file.
